This application claims the benefit of Korean Patent Application Nos. 10-2005-0002863 and 10-2006-0002650 filed Jan. 12, 2005 and Jan. 10, 2006, respectively, in Korea, which are hereby incorporated by reference in their entirety.
(a) Field of the Invention
The present invention relates to a gasketed membrane-electrode assembly, and a fuel cell system comprising the same. Because the gasket and membrane-electrode assembly is provided as a single body, leakage of gases such as fuel gas and oxidizing gas decrease when operating the fuel cell. Various materials can be selected for preparing each layer, and a process of manufacturing a fuel cell therewith is simple, and thus the gasketed membrane-electrode assembly is suitable for mass production of fuel cells.
(b) Description of the Related Art
Fuel cells have recently become more important as a new power generation system. In the near future, fuel cells may replace the currently-used electric power sources for automobiles, for residential power generators, and for portable products.
A polymer electrolyte fuel cell is a direct current power generator that transforms chemical energy of a fuel into electrical energy through an electrochemical reaction. The fuel cell is a continuous complex comprising a membrane-electrode assembly (MEA) as a heart of the fuel cell, and a separator (or bipolar plate) that collects the electricity and provides the fuel. The membrane-electrode assembly is a joint body of a polymer membrane where hydrogen ions are transferred, and an electrode where a methanol solution or a fuel such as hydrogen reacts with air through an electrochemical catalytic reaction.
The electrochemical reaction consists of two separate reactions, which are an electrochemical oxidation reaction at a fuel electrode and an electrochemical reduction reaction at an air electrode. The fuel electrode and air electrode are separated by an electrolyte. In a direct methanol fuel cell, the fuel electrode is supplied with methanol and water instead of hydrogen, hydrogen ions generated in the process of methanol oxidation move to the air electrode along the polymer electrolyte, and then the reduction reaction with oxygen supplied from the air electrode occurs to produce electricity.
If a fuel or oxidizing agent supplied from each electrode passes through the electrolyte membrane, it has a negative effect on the performance of the fuel cell. Accordingly, it is necessary to prevent fuel and oxidizing gas from passing through the electrolyte membrane and mixing. The ability of prevention of mixing of the fuel and oxidizing gas is related to the properties of the polymer electrolyte membrane. In this regard, a gasket is arranged on the circumferential part of the membrane-electrode assembly that is outside of the electrode area, thereby preventing the fuel or oxidizing gas from passing through the membrane and mixing. However, because the electrolyte membrane is very expensive, the circumferential part of the electrolyte membrane in the membrane-electrode assembly is replaced with a new gasket to reduce the price of the fuel cell.
In addition, it is usual for the conventional assembly of the electrolyte membrane and the gasket to be manufactured by a molding method. The molding method is not suitable for continuous mass production, and the gasket that directly contacts the electrolyte membrane must be made from only halogenated resin having resistance to acid due to the acidity of the electrolyte membrane.
U.S. Pat. No. 6,316,139 discloses a united membrane-electrode assembly interposed between a pair of gaskets each consisting of an elastomer layer and an adhesive layer.
JP H09-097619 discloses a united membrane-electrode assembly interposed between a pair of gaskets which includes an elastic layer formed on an acrylic substrate, and the acrylic substrate is adhered to one side of the separator through an adhesive layer.
JP 2002-329512 discloses a gasket for a fuel cell where the gasket body is made from elastic material units with a stacked film of a resin film, an adhesive agent, and a releasing film. By peeling off the releasing film, the gasket is arranged on the polymer electrolyte membrane with an adhesive agent. However, in the method, only a part of the releasing film is removed, thereby decreasing adhesiveness between the polymer electrolyte membrane and gasket.